The former Benfica star, who came close to a summer move to Manchester United, faces a spell on the sidelines after picking up an ankle injury in the win over Rayo Vallecano
The Portugal international picked up the knock in Madrid's 3-2 Liga win over Rayo Vallecano and was forced to leave the pitch in the dying minutes of the first half of the encounter.
The 25-year-old was then examined to determine the extent of the injury and Madrid have now announced that Coentrao will be out of action while he is assessed further.
"After tests carried out on Fabio Coentrao at the Sanitas La Moraleja Hospital, it has been confirmed that he has a sprained left ankle, which will continue to be monitored," a statement on the club's official website reads.
Coentrao's absence means that Marcelo is likely to be reinstated at left-back for Tuesday's match in Turin after he was rested for the game against Rayo.
Madrid currently sit atop of Group B with nine points from three games and will qualify for the knockout stages with a win over Juve.